The infrared (IR) spectral region is of interest for a number of reasons. For example, the frequency peak of the blackbody radiation spectrum at room temperature is at ˜30 THz. Thus, at typical ambient temperatures objects continually exchange energy with the radiation field at IR frequencies. Therefore, there is significant information about properties such as the temperature, emissivity, etc. of objects in our environment contained in the IR radiation field.
At night, this radiation may be used to visualize the environment and to find particularly “hot” objects—such as, for example, people and engines. This application has made the IR spectral region important for defense applications, leading the military to have had a long-standing focus on improving infrared technology.
Additionally, the atmosphere is somewhat transparent in two different IR spectral windows (MWIR: mid-wave IR ˜60-100 THz, and LWIR: long-wave IR ˜25-40 THz), making these ranges particularly interesting.
Furthermore, many common molecular vibrations are in the IR, e.g., the vibrational mode of a hydrogen molecule is ˜120 THz and the C-H stretch vibration (of interest because most organic compounds have a signature in this frequency range) is ˜90 THz, while heavier and more complex molecules have signatures at lower frequencies. For example the P—O stretch, that is a signature of many nerve agents, is ˜30 THz.
Therefore, there is, and will continue to be, significant interest in detecting and monitoring radiation across the IR spectral range and new methods and sensors for performing these functions are continually sought. Exemplary embodiments of the present invention include frequency selective IR photodetectors, rectennas, focal plane arrays, and waveguide sensors to help meet the demand for various forms of frequency selective IR sensors.